BeveledRectangleBorder constructor
Creates a border like a RoundedRectangleBorder except that the corners are joined by straight lines instead of arcs.
The arguments must not be null.
Implementation
const BeveledRectangleBorder({
this.side = BorderSide.none,
this.borderRadius = BorderRadius.zero,
}) : assert(side != null),
assert(borderRadius != null);